Orbitread builders, and other tread builders of a similar type, utilise an elongate, continuous strip of a suitable rubber compound which is extruded into a suitable tread strip form in which it can be applied onto an existing buffed tire, to be retreaded, in a continuous manner to form the new tread area of the tire. After such application, special tread formations can be formed in the tread rubber and the retreading can then be completed by curing the newly applied tread, whereby its required wear qualities are attained.
Generally, with tread builders of the above type, the original strip of a suitable rubber compound is fed into a screw or worm conveyor which conveys the compound towards an extrusion die through which it is forced to form the strip or tread to be applied onto a tire. The operation of such tread builders, hereinafter merely referred to as "tread builders", is not described in any further detail herein since it does not form an essential part of the present invention.
It is known to the Applicants that one major waste product resulting from the retreading of tires is rubber dust or crumbs. Such dust or crumbs in particular result from the buffing of tires before a new tread layer is applied, in order to form a suitable surface for receiving such a tread layer. Rubber dust or crumbs can clearly also be provided as a result of other processes which relate particularly to the tire industry, or the like. Usually such dust or crumbs go to waste but as it is often of a suitable rubber compound used for tires, attempts have been made to employ such dust or crumbs for forming a tread strip which can be utilised to form the new tread layer of a tire during retreading.
One particular method of utilising rubber dust or crumbs in the above manner has been to provide a feeding device, which can cooperate with tread builders, to feed rubber dust or crumbs into the screw or form conveyor of the tread builders, so that it is combined with the conventionally used strip of a suitable rubber compound to be extruded into a tread strip form, as above described. One proposed feeding device for the above purpose includes a box-like feed hopper for containing the rubber dust or crumbs and a screw conveyor disposed beneath an opening in the hopper to convey rubber dust or crumbs to an outlet from which it can be fed into the screw conveyor of the tread builder.
Because of the tendency of rubber dust or crumbs to adhere together and compact, no success has been attained in providing a continuous feed of rubber dust or crumbs to the tread builder, despite the use of a conventional type agitator, located in the hopper, taking the form of a rotatable shaft having rubber fingers projecting therefrom to continuously agitate the rubber dust or crumbs. For the above reasons and to the knowledge of the Applicants, the proposed use of rubber dust or crumbs has never been commercially accepted and suitable feeding devices have never been perfected and sold.